package com.xuehu.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * 统计网站在线人数: 统计session
 */
public class OnlineCountListener implements HttpSessionListener {

    //创建session监听: 看你的一举一动
    //一旦创建一个session就会触发一次这个事件
    public void sessionCreated(HttpSessionEvent se) {
        ServletContext servletContext = se.getSession().getServletContext();
        Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount");

        if (onlineCount == null) {
            onlineCount = new Integer(1);
        } else {
            int count = onlineCount.intValue();

            onlineCount = new Integer(count + 1);

        }

        servletContext.setAttribute("OnlineCount", onlineCount);

    }

    //销毁session监听
    //一旦销毁Session就会触发一次这个事件!
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext ctx = se.getSession().getServletContext();

        Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");

        if (onlineCount == null) {
            onlineCount = new Integer(0);
        } else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count - 1);
        }

        ctx.setAttribute("OnlineCount", onlineCount);

    }

    /**
     * Session的销毁
     * 1.手动销毁
     * 2.自动销毁
     */
}
